class I2C – a two-wire serial protocol¶
I2C is a two-wire protocol for communicating between devices. At the physical level it consists of 2 wires: SCL and SDA, the clock and data lines respectively. OpenMV Cam does not provide Pullups on the SDA or SCL lines and external pullups are required on both SDA and SCL lines for the I2C bus to be functional.
I2C objects are created attached to a specific bus. They can be initialised when created, or initialised later on.
Example:
from pyb import I2C
i2c = I2C(2) # create on bus 2
i2c = I2C(2, I2C.MASTER) # create and init as a master
i2c.init(I2C.MASTER, baudrate=20000) # init as a master
i2c.init(I2C.SLAVE, addr=0x42) # init as a slave with given address
i2c.deinit() # turn off the peripheral
Printing the i2c object gives you information about its configuration.
The basic methods are send and recv:
i2c.send('abc') # send 3 bytes
i2c.send(0x42) # send a single byte, given by the number
data = i2c.recv(3) # receive 3 bytes
To receive inplace, first create a bytearray:
data = bytearray(3) # create a buffer
i2c.recv(data) # receive 3 bytes, writing them into data
You can specify a timeout (in ms):
i2c.send(b'123', timeout=2000) # timeout after 2 seconds
A controller must specify the recipient’s address:
i2c.init(I2C.CONTROLLER)
i2c.send('123', 0x42) # send 3 bytes to peripheral with address 0x42
i2c.send(b'456', addr=0x42) # keyword for address
Master also has other methods:
i2c.is_ready(0x42) # check if peripheral 0x42 is ready
i2c.scan() # scan for peripherals on the bus, returning
# a list of valid addresses
i2c.mem_read(3, 0x42, 2) # read 3 bytes from memory of peripheral 0x42,
# starting at address 2 in the peripheral
i2c.mem_write('abc', 0x42, 2, timeout=1000) # write 'abc' (3 bytes) to memory of peripheral 0x42
# starting at address 2 in the peripheral, timeout after 1 second
Constructors¶
- class pyb.I2C(bus, ...)¶
Construct an I2C object on the given bus.
bus
can be 2 or 4. With no additional parameters, the I2C object is created but not initialised (it has the settings from the last initialisation of the bus, if any). If extra arguments are given, the bus is initialised. Seeinit
for parameters of initialisation.The physical pins of the I2C buses on the OpenMV Cam are:
I2C(2)
is on the Y position:(SCL, SDA) = (P4, P5) = (PB10, PB11)
The physical pins of the I2C buses on the OpenMV Cam M7 are:
I2C(2)
is on the Y position:(SCL, SDA) = (P4, P5) = (PB10, PB11)
I2C(4)
is on the Y position:(SCL, SDA) = (P7, P8) = (PD12, PD13)
Methods¶
- I2C.deinit()¶
Turn off the I2C bus.
- I2C.init(mode, *, addr=0x12, baudrate=400000, gencall=False, dma=False)¶
Initialise the I2C bus with the given parameters:
mode
must be eitherI2C.CONTROLLER
orI2C.PERIPHERAL
addr
is the 7-bit address (only sensible for a peripheral)baudrate
is the SCL clock rate (only sensible for a controller)gencall
is whether to support general call modedma
is whether to allow the use of DMA for the I2C transfers (note that DMA transfers have more precise timing but currently do not handle bus errors properly)
The actual clock frequency may be lower than the requested frequency. This is dependent on the platform hardware. The actual rate may be determined by printing the I2C object.
- I2C.is_ready(addr)¶
Check if an I2C device responds to the given address. Only valid when in controller mode.
- I2C.mem_read(data, addr, memaddr, *, timeout=5000, addr_size=8)¶
Read from the memory of an I2C device:
data
can be an integer (number of bytes to read) or a buffer to read intoaddr
is the I2C device addressmemaddr
is the memory location within the I2C devicetimeout
is the timeout in milliseconds to wait for the readaddr_size
selects width of memaddr: 8 or 16 bits
Returns the read data. This is only valid in controller mode.
- I2C.mem_write(data, addr, memaddr, *, timeout=5000, addr_size=8)¶
Write to the memory of an I2C device:
data
can be an integer or a buffer to write fromaddr
is the I2C device addressmemaddr
is the memory location within the I2C devicetimeout
is the timeout in milliseconds to wait for the writeaddr_size
selects width of memaddr: 8 or 16 bits
Returns
None
. This is only valid in controller mode.
- I2C.recv(recv, addr=0x00, *, timeout=5000)¶
Receive data on the bus:
recv
can be an integer, which is the number of bytes to receive, or a mutable buffer, which will be filled with received bytesaddr
is the address to receive from (only required in controller mode)timeout
is the timeout in milliseconds to wait for the receive
Return value: if
recv
is an integer then a new buffer of the bytes received, otherwise the same buffer that was passed in torecv
.
- I2C.send(send, addr=0x00, *, timeout=5000)¶
Send data on the bus:
send
is the data to send (an integer to send, or a buffer object)addr
is the address to send to (only required in controller mode)timeout
is the timeout in milliseconds to wait for the send
Return value:
None
.
- I2C.scan()¶
Scan all I2C addresses from 0x01 to 0x7f and return a list of those that respond. Only valid when in controller mode.
Constants¶
- I2C.CONTROLLER¶
for initialising the bus to controller mode
- I2C.PERIPHERAL¶
for initialising the bus to peripheral mode